Bachelor Projects 2019

Dark Matter

XAMS

The Nikhef dark matter group has a small version of the XENON1T detector in the lab. With this detector which is more than a factor 1000 smaller than the newly built XENON1T detector in Gran Sasso we (i) investigate the properties of xenon as a detector, and (ii) aim to improve the methods we use in the XENON1T experiment to detect dark matter. The principles of operation of this smal detector are identical to its big sibling in Gran Sasso.
We are looking for a student interested in dark matter physics, and with a focus on working in the lab (hands-on profile). The student will work with the new AmBe neutron source and liquid scintillatorneutron detector we have acquired for the project. With such a source we can generate signals in our lab setup that ar identical to the signals we expect from real dark matter interactions in xenon. The goal of this project will be to do the first measurements with the neutron source and analyze the data. Depending on the progress with the hardware we intend to complement the measurements with Monte Carlo study of neutron transport in xenon.
Supervisors: A.P. Colijn (colijn_at_nikhef.nl)

Backgrounds in Radioactive Decay Measurements

At Nikhef, the XENON group has a working setup, continuously monitoring the
radioactive decay of Cobalt-60, Caesium-137 and Titanium-44. This beautiful setup is
however not shielded perfectly; it is still vulnerable to background radioactivity. Our
current way of working around this background radiation is to subtract it from our
waveforms. You as a BSc student could help us hands-on and with analyses:
together, we can disassemble the setup, measure background spectra and
implement this in the data analysis. You can use all the data to validate the
lifetime of our isotopes!

Machine learning

Machine learning has proven to be an indispensable tool in the selection of interesting events in high energy physics. Such technologies will become increasingly important as detector upgrades are introduced and data rates increase by orders of magnitude. HEPDrone is a toolkit to enable the creation of a drone classifier from any machine learning classifier, such that different classifiers may be standardised into a single form and executed in parallel. A detailed evaluation of the performance of different drone models in the real production environment of LHCb will give the collaboration a complete idea of not only the advantages of the drone model, but also the limits of drone complexity given the available computing resources.
Requirements: Advanced python and Advanced C++
Supervisor: Sean Benson

LHCb simulations of physics beyond the Standard Model

This project is of relatively theoretical and computing nature and performs simulation studies for physics beyond the Standard Model in the context of long lived particles. It is related to test the sensitivity of the LHCb experiment to detect specific signals of physics beyond the Standard Model.
supervisor: Carlos Vazquez Sierra

Muon tomography

In this project we are not looking for where cosmic rays come from. We are looking for what we can use them for instead. The muons in cosmic rays can be used to ‘probe’ massive objects. Muons are short lived particles that carry the same charge as electrons, have a high penetrating power and can be detected relatively easy. It is possible to reconstruct a density distribution within an object by measuring muon scattering and absorption. In this context the objects may be freight containers, buildings, melting furnaces, etc…

Systems that scan objects through the use of muons are often large (objects often need to be enclosed by the system) and complex. The question we want to answer is: Can we develop a smaller, simpler and cheaper system for muon tomography?

A method to detect muons is by using a material that scintillates (emits light) when hit by an ionising particle. When this light emission is prompt after the passage of the muon, timing information of the light can be used to reconstruct the path of the muon.
In this experiment we make a muon tracker based on two sheets of scintillating material and photo multiplier tubes (PMTs). Photo multiplier tubes are fast responding and very sensitive light detectors (capable of detecting single photons).

The big question is: How well does this system perform?

Currently a set-up is being build. You have a lot of freedom to choose a focus in this project (theory, simulation, hardware, or a combination of those).

Supervisor: Martin Fransen

Spectral X-ray imaging - Looking at colours the eyes can't see

When a conventional X-ray image is made to analyse the composition of a sample, or to perform a medical examination on a patient, one acquires an image that only shows intensities. One obtains a ‘black and white’ image. Most of the information carried by the photon energy is lost. Lacking spectral information can result in an ambiguity between material composition and amount of material in the sample. If the X-ray intensity as a function of the energy can be measured (i.e. a ‘colour’ X-ray image) more information can be obtained from a sample. This translates to less required dose and/or to a better understanding of the sample that is being investigated. For example, two fields that can benefit from spectral X-ray imaging are mammography and real time CT.

X-ray detectors based on Medipix/Timepix pixel chips have spectral resolving capabilities and can be used to make polychromatic X-ray images. Medipix and Timepix chips have branched from pixel chips developed for detectors for high energy physics collider experiments.

Some themes that students can work on:

- Optimising methods to acquire spectral X-ray images.

- Determining how much existing applications benefit from spectral X-ray imaging and looking for potential new applications.

Holographic emitter

A difficulty in generating holograms (based on the interference of light) is the required dense spatial light field sampling. One would need pixels of less than 200 nanometer. With larger pixels artefacts occur due to spatial under sampling. A pixel pitch of 200 nm or less is difficult, if not, impossible, to achieve, especially for larger areas. Another challenge is the massive amount of computing power that is required to control such a dense pixel matrix.

A new holographic projection method has been developed that reduces under sampling artefacts, regardless of spatial sample density. The trick is to create 'pixels' at random but known positions, resulting in an array that lacks any spatial periodicity. As a result a holographic emitter can be built with a significantly lower sample density and less required computing power. This could bring holography in reach for many applications like display, lithography, 3D printing, metrology, etc...

The big question: How does the performance of the holographic emitter depend on sample density and sample positions?

The aspects of a holographic image we are interested in are:

- Noise

- Contrast

- Suppression of under sampling artefacts

- Resolution

For this project we are building a proof of concept holographic emitter. This set-up will be used to verify simulation results (and to make some cool holograms of course).

Supervisor: Martin Fransen

KM3NeT

The KM3NeT collaboration is constructing a new generation neutrino telescope with a volume of
several cubic kilometers (final configuration) in the deep waters of the Mediterranean Sea. With the data,
scientists will look for the astrophysical sources of neutrinos such as supernovae, colliding stars or gamma-ray
bursts. In the domain of particle physics the properties of neutrinos will be investigated, in particular the unknown
neutrino mass hierarchy.

The KM3NeT telescope detects the Cherenkov light emitted by the secondary particles produced in neutrino
interactions using an array of thousands of sensitive 3 inch photo-multiplier tubes housed in 17 inch pressure
resistant glass spheres, digital-optical-modules (DOMs), together with electronics. The DOMs are oriented along
700m long vertical lines, called detection units.

Data analysis of the first deployed KM3NeT detection lines

First detection lines of the KM3NeT neutrino telescope have been deployed
in the Mediterranean Sea, and a first data set is available. The lines consist
of light-sensitive detectors that record the time of arrival of photons
produced by relativistic particles in the deep sea, and their number.
In this project we will study the first data to separate various components:
photons from potassium decay, bioluminesence, sparks in the photomultipliers,
downgoing muons from cosmic rays, and perhaps first neutrinos.

Supervisors: Ronald Bruijn, Paul de Jong and Dorothea Samtleben

Neutrino oscillation measurements with the KM3NeT neutrino telescope

The ORCA block of the KM3NeT neutrino telescope currently under construction
will be able to measure the oscillations of neutrinos produced in interactions
of cosmic rays with the earth atmosphere. Fundamental neutrino properties can
be deduced from these oscillations measurements, in particular the so-called
mass hierarchy of neutrinos. In this project we will simulate the ORCA measurements
of neutrino oscillations, and study the dependence of the sensitivity on
experimental uncertainties, such as energy resolution and neutrino flavour
identification, and theoretical uncertainties, such as the atmospheric neutrino
flux and neutrino cross sections. The results will help ORCA to identify
the main sources of uncertainty, and therefore to actively try to reduce these
and improve the final measurement.

Supervisors: Ronald Bruijn, Paul de Jong and Dorothea Samtleben

VIRGO

The Advanced LIGO and Advanced Virgo interferometers have recently observed gravitational waves from binary neutron star mergers. Prior to merger, as two neutron stars spiral towards each other, the tidal field of one star will cause a deformation in the other. These deformations affect the orbital motion, which in turn gets imprinted onto the gravitational wave signal. This way we can find out how deformable a neutron star is in the first place, which will yield information about the interior of neutron stars; the latter is the main open problem in nuclear astrophysics.

To succeed in this, good models are needed for the gravitational waveforms. The best model currently available which can be generated sufficiently fast on a computer to be useful in data analysis, contains a state-of-the art description of tidal effects, but not neutron star spins. It is generally assumed that neutron stars are slowly spinning, but it needs to be determined how measurements of tides would be affected by the absence of spins in our analyses.

In practice, the project will consist of learning how to use pre-existing gravitational wave data analysis tools, setting up simulations based on them, and interpreting the results.

The VIRGO collaboration operates the advanced VIRGO gravitational waves detector in Italy, and forms together with the LIGO collaboration a consortium that analyzes the data from both VIRGO and LIGO. For projects in the Nikhef VIRGO group, please contact Frank Linde (frank.linde_at_nikhef.nl) or Chris van den Broeck (vdbroeck_at_nikhef.nl)

Bachelor Projects 2017

The Cherenkov Telescope Array (CTA) is a planned facility for measuring gamma rays from space covering more than four orders of magnitude in energy, up to energies exceeding 100 TeV. CTA employs the imaging atmospheric Cherenkov technique to measure properties of cosmic gamma rays. This technique is based on measuring Cherenkov light emitted during the development of a gamma-ray air shower. CTA will be built at two experimental sites, one in the Northern, one in the Southern hemisphere, and will consist of up to 100 telescopes. It represents a major leap forward in sensitivity and precision for gamma-ray astronomy, and will allow us to explore very-high-energy processes of the extreme Universe at an unprecedented level.

Two projects for students are available at the CTA group of UvA in the field of optical and photonic R&D contributing to the starting phase of CTA. For the first project the student will conduct measurements to characterise novel kinds of single-photon detectors, referred to as silicon photomultipliers, and evaluate different types of these sensors for their use for CTA. For the second project the student will develop and test an imaging system making use of a liquid crystal display. This flexible light source will be able to mimic images from different light sources of the night sky as seen by cameras of CTA, for instance gamma-ray air showers or stars, and will be used for camera tests and calibration.

Supervisors: David Berge, Maurice Stephan (postdoc)

Dark Matter

The discovery of neutrino oscillation (Nobel Physics 2015) means that neutrinos have mass. We already know that their masses are tiny, more than one million times smaller than the next-lightest particle in the standard model, the electron. This raises the question if the mass-generation mechanism is the same for neutrinos as it is for the other subatomic particles. In particular, since neutrinos are electrically neutral, they could be their own anti-particles - we call these types of particles Majorana. The only practical way to discover if neutrinos are Majorana is through the search of an extremely rare radioactive decay called neutrinoless double beta decay (0n2b). A few isotopes are candidates for this process, among them Xe-136. The natural abundance of Xe-136 in natural xenon is about 9%, and this gives the opportunity to look for a 0n2b signal in xenon-based dark matter detectors like XENON1T and the future XENONnT and DARWIN detectors.

We are looking for a student interested in doing a sensitivity study for 0n2b in XENONnT and the DARWIN experiments. The first goal will be to understand the physics addressed in neutrinoless double beta decay. Then the student will inventory possible backgrounds for the signal, use a (controversial) claim of a 0n2b signal as a benchmark and finally obtain the sensitivity of these future detectors. The work will involve simulations and analysis, building on an existing framework developed in our group.

Supervisors: M.P. Decowski & A. Tiseni

Shaking Dark Matter detectors

Our XENON1T detector is built in the lab underneath the Gran Sasso mountains in central Italy. The lab is very well suited for low-background experiments due to the 1.5km of rock overburden.
However, as you may know, cental Italy has been plagued by earthqaukes over the past decade, with the most recentones occurring in January 2017. We need a BSc student to investigate the
details of such earthquakes in our underground lab. What are the magnitdues by which stuff is moving underground? What are the accelerations? What is the potential effect on our experimental
setup? What would ahppen if an earthquake happens much closer to our lab? Furthermore we are interested to find out whether Earthquakes can be predicted. Some papers claim that before
an earthquake the radon emanating from rock increases. In our lab we measure the radon concentration as a function of time: can you find a correlation between the measurements and recent
earthquakes?

If you are interested in finding out more about earthquakes, please contact M.P. Decowski or A.P. Colijn

XAMS - a baby dark matter detector

The Nikhef dark matter group has a small version of the XENON1T detector in the lab. With this detector which is more than a factor 1000 smaller than the newly built XENON1T detector in Gran Sasso
we (i) investigate the properties of xenon as a detector, and (ii) aim to improve the methods we use in the XENON1T experiment to detect dark matter. The principles of operation of this smal detector
are identical to its big sibling in Gran Sasso.

We are looking for a student interested in dark matter physics, and with a focus on working in the lab (hands-on profile). The student will work with the new AmBe neutron source we have acquired
before the start of the project. With such a source we can generate signals in our lab setup that ar identical to the signals we expect from real dark matter interactions in xenon. The goal of this project
will be to do the first measurements with the neutron source and analyze the data. Depending on the progress with the hardware we intend to complement the measurements with Monte Carlo study
of neutron transport in xenon.

Supervisors: A.P. Colijn & E. Hogenbirk

Radon is bad for Dark Matter

Radon is the dominant background for xenon based dark matter detectors, like the XENON1T experiment. In our lab at Nikhef we are investigating ways to reduce or eliminate the effect of radon
on our sensitivity. For our lab setup XAMS we have designed and constructed a radon detector, that can be used in xenon systems at high-pressure. This completely new detector
is now waiting for a BSc student to fully chracterize and use it. During this project you will first study the effect that radon contaminations have on dark matter detectors, then you will start working to
understand our new radon detector in detail. You will learn howto use a radioactive source to calibrate the detector: this is something which is not easy and has not been done before in our lab.
If you manage to succesfully calibrate the detector, we then want to incorporate it into our lab xenon system at Nikhef and maybe at some later stage in the real XENON1T detector!

The profile of the student to work on this project is broad. I expect a good theoretical knowledge in order to quickly get upto speed with understanding dark mater detectors, and in addition I
need 'lab-creativity' in order to develop methods for calibrating the new detector. If a good method is developed, it will be used for many years by the Nikhef dark matter group and beyond.

Supervisors: A.P. Colijn & E. Hogenbirk

ATLAS

ATLAS (1): Searching for new physics with the Higgs and W bosons

The strength of the Higgs interactions with electroweak bosons are precisely defined in the
Standard Model. Therefore they are sensitive probes of the mechanism of electroweak symmetry
breaking and enable searches for new physics beyond the SM. With the data collected by the ATLAS
experiment in years 2015-2016 we plan to measure separately the Higgs coupling to
longitudinally and transversely polarised W bosons in a process of weak boson fusion. To
maximise experimental sensitivity we are developing techniques to separate the signal from
background processes. You will take part in investigating possible improvements from
reconstructing events in reference frames boosted with respect to the detector. During the
project you will learn modern experimental analysis techniques. This project is a part of Vector
Boson Scattering Coordination and Action Network (VBSCan) which connects researchers studying
this and related topics worldwide.

Supervisors: Pamela Ferrari, Magdalena Slawinska, Bob van Eijk

ATLAS (2): Dark-matter-motivated searches for supersymmetric particles at the LHC

Supersymmetry, a symmetry between fermions and bosons in particle physics,
may provide a particle that could be the dark matter in the universe.
The observation of an excess of gamma rays originating from the centre of our
galaxy could be explained in a model where supersymmetric dark matter
particles annihilate each other in the galactic centre, leading to gamma rays.

Given the model parameters, it should also be possible to produce such
particles at the LHC, at CERN in Geneva. But it is not so easy to observe
them: the signal is small, and the noise (background) is large.
In this project, we will use simulations of signal and background to
optimize experimental searches for such particles with the ATLAS detector,
apply them to the data collected in 2015, and prepare for the new data in
2016 and later.Where possible, we will explore new machine learning techniques.

One of the key sub-systems of the ATLAS experiment at the Large
Hadron Collider (LHC) is the Inner Detector (ID), designed to provide
excellent charged particles momentum and vertex resolution measurements.

At Phase-2 of the LHC run, in ~2025, the operating luminosity of
the collider will be increased significantly.
This will imply an upgrade of all ATLAS subsystems. In particular,
the ID will be fully replaced with a tracker completely made of
Silicon, having higher granularity and radiation hardness.
The R&D process for the new ATLAS ID is now ongoing.
Different geometrical layouts are simulated and their performance is
studied under different operating conditions in search for the optimal
detector architecture. Also, the performance of the new
Si-sensors/modules is under investigation with dedicated laboratory tests.

The focus of the project could be on the simulation of the High-Luminosity LHC
version of the ATLAS Inner Detector. The student will learn how a
high-energy physics experiment is designed and optimized.
Alternatively, if possible at that moment, the student could
work on a project at the Nikhef Silicon laboratory at the test-bench for
new ATLAS Si-strip detectors and participate in the quality
assurance procedure for the new ATLAS Si detectors.

KM3Net

The KM3NeT collaboration is constructing a new generation neutrino telescope with a volume of
several cubic kilometers (final configuration) in the deep waters of the Mediterranean Sea. With the data,
scientists will look for the astrophysical sources of neutrinos such as supernovae, colliding stars or gamma-ray
bursts. In the domain of particle physics the properties of neutrinos will be investigated, in particular the unknown
neutrino mass hierachy.

The KM3NeT telescope detects the Cherenkov light emitted by the secondary particles produced in neutrino
interactions using an array of thousands of sensitive 3 inch photo-multiplier tubes housed in 17 inch pressure
resistant glass spheres, digital-optical-modules (DOMs), together with electronics. The DOMs are oriented along
700m long vertical lines, called detection units.

The first phase of the KM3NeT neutrino telescope is currently under construction, with the first two detection units operational at 3500m depth in the Mediterranean Sea, 100 km off the coast of Sicily.

KM3NeT (1): Photon counting in KM3NeT

The details of a neutrino interaction, such as its incoming direction and energy, determine the pattern, time and amount, of recorded photons (´hits´) by the photo-multplier tubes. The time of arrival is recorded with nanosecond accuracy and the amount of photons is encoded in the length of the pulse(time-over-threshold, ToT). Currently, only the photon arrival time and the number of photo-multipliers that record a hit are used in reconstructing event properties.
In this project, the distributions of the ToT mainly originating from photons from potassium-40 decays in the sea-water and from atmospheric muons passing through the water will be studied. The goals are to investigate the properties of the ToT distributions obtained from data and simulation, in particular the dependence on the photo-multiplier efficiency and atmospheric muon flux.
In this project we will be extensively using the programming language C++ to analyse the data, so a reasonable proficiency is required.

Supervisors: Ronald Bruijn & Karel Melis

Email: rbruijn_at_nikhef.nl

VIRGO

"It is anticipated that in the next few years, Advanced LIGO and Advanced Virgo will start observing gravitational waves from binary neutron star mergers. Prior to merger, as two neutron stars spiral towards each other, the tidal field of one star will cause a deformation in the other. These deformations affect the orbital motion, which in turn gets imprinted onto the gravitational wave signal. This way we can find out how deformable a neutron star is in the first place, which will yield information about the interior of neutron stars; the latter is the main open problem in nuclear astrophysics.

To succeed in this, good models are needed for the gravitational waveforms. The best model currently available which can be generated sufficiently fast on a computer to be useful in data analysis, contains a state-of-the art description of tidal effects, but not neutron star spins. It is generally assumed that neutron stars are slowly spinning, but it needs to be determined how measurements of tides would be affected by the absence of spins in our analyses.

In practice, the project will consist of learning how to use pre-existing gravitational wave data analysis tools, setting up simulations based on them, and interpreting the results."

The VIRGO collaboration operates the advanced VIRGO gravitational waves detector in Italy, and forms together with the LIGO collaboration a consortium that analyzes the data from both VIRGO and LIGO. For projects in the Nikhef VIRGO group, please contact Jo van den Brand (jo_at_nikhef.nl) or Chris van den Broeck (vdbroeck_at_nikhef.nl)

LHCb

Begeleider: Sean Benson

Title:
Searching for physics beyond the Standard Model with LHCb

The LHCb experiment is designed to study the "The Flavour Problem" in particle physics:
Why is the universe dominated by matter over antimatter? Why are there three generations of elementary particles? What is the origin of quark flavour changing interactions.

To solve these riddles, LHCb performs precision measurements on b-quark particle decays.
An intriguing signal has recently been observed in the decay of a B-meson to a K* and two muons: Bd→K*μμ, which does not seem to behave according to the predictions of the Standard Model
In this project the bachelor student will investigate this further by studying the case where the K* particle decays to a so-called k-short particle and a π0. The observation of such a final state will provide valuable information in the search for physics beyond the Standard Model.

In this ambitious project the student is expected to study both a theory on the mechanism of CP violation with B mesons, in addition to data analysis with B decays. Programming experience in python is required.

The LHCb experiment at CERN analyzes the properties of B-hadrons produced in proton-proton collisions at the LHC. For projects in the LHCb group, please contact Marcel Mark (marcel.merk_at_nikhef.nl)